Signs of dementia. No- losing our car keys is not a sign of dementia. This is a very common problem. No one would suspect dementia based on this symptom.
Signs of dementia include difficulty with memory, language, drawing, calculations, planning, making lists and completing complex tasks. A good example is forgetting to care for personal hygeine, clean your home or shop for food for may days.

Not necessarily. Trouble forming a new memory, getting lost in familiar places and word finding problems are the most common signs of alzheimers. To diagnose dementia one needs to look for multiple symptoms i n different parts of the brain that are affecting functioning.

Maybe. Everybody loses their car keys or forgets a name or can't remember what they did yesterday.... Some times. Some people habitually lose things, forget things, or space out, but that's just who they are. Dementia is persistent loss in cognitive ability or function.
What was the question, again?